Patent GB-400014-A (GB)
Title: Electric selective receiving apparatus responsive to code signals
IPC: H04L15/26
Filed: 1932-12-13
Abstract: 400,014. Selectors responsive to code signals. LITSTRÍM, A. S., 24, Sibyllegatan, Stockholm. Dec. 13, 1932, No. 35345. Convention date, Dec. 14, 1931. [Class 40 (iv).] A selector responsive only to signals comprising marks of substantially equal length separated by intervals of substantially equal length comprises two timing devices, one of which checks the minimum length of the marks while the other checks firstly the difference between minimum and maximum duration of the marks, and subsequently, the maximum duration of the intervals. The second timer, during its operation to check intervals, is independent of the signal receiving relay and therefore of interfering signals. The tolerances are such that the two last mentioned time periods are equal. The timing devices may be vibrators, dash-pots, thermal or photo-electric devices but, as described, comprise condensers adapted to be charged until a common discharge tube strikes. Operation for correct signals. Relay 1 pulls on receipt of the first mark, operates relay 3, and removes a short-circuit from condenser 15 which charges up from battery 20. When the mark has persisted for the minimum duration, the condenser 15 has charged to a potential sufficient to discharge over glow lamp 30 and operate relay 4 (upper) which locks over its lower winding and energizes relays 5, 9, of which 9 locks up. Relay 3 falls back owing to a short-circuit by 5, and 9 energizes a winding 101 of a register which pulls the pawl 107 into contact with ratchet wheel 103. Relay 2 (lower), operated by 5, disconnects a short circuit from condenser 25 which commences to charge up, but if the mark has not exceeded the maximum duration when 1 falls back, relay 2 relapses to discharge condenser 25, 8 pulls up, locks and short-circuits the holding winding of 4 so that 4 and 5 fall back, and relay 2 pulls up over its upper winding to charge condenser 25 for measuring the pause. Relay 8 also energizes stepping magnet 102 to advance the ratchet wheel one step. Assuming that the next mark comes in before maximum pause duration has elapsed, relay 1 pulls up and commences to charge 15 but nothing further happens at present since 3 is short-circuited by 8. After the prescribed maximum pause interval, however, condenser 25 discharges over lamp 30 and operates relay 7 (upper) which holds over its lower winding, and short-circuits the holding winding of 8 which removes the short-circuit on 3, releases 2 and de-energizes the stepping magnet. Relay 3 thereupon operates and the cycle of operations ensuing on the receipt of the first mark is repeated, relay 7 being released when condenser 15 discharges to operate relay 4. When the ratchet wheel has stepped three times, cam-operated contacts 109 give the alarm over 110. Rejection of incorrect signals. Short initial disturbing and other signals not exceeding the minimum mark duration are without effect since condenser does not receive a sufficient charge and 3 falls back when 1 relapses. If a short signal occurs during the second or subsequent mark period (relays 7, 9 and pull down winding 101 also operated), 9 (lower) is short-circuited when 1 falls back and releases 7 and 101. If the mark lasts too long, condenser 25 discharges over 7 before the end of the mark and as relays 2, 4, 5, 9 and winding 101 are energized in addition to 1 and 3 at this time, 6 (upper) pulls up and locks over its lower winding until 1 falls back. Relay 6 releases 4 and 5, and 2, 9, 101 thereupon relapse. When the mark ceases 1 relapses followed by 3 and 6. If a pause is too long (2, 8, 9 operated, both windings 101, 102 energized, and 1 unoperated), the operation of 7 by discharge of condenser 25 short-circuits 9 (lower) which releases the operated relays and windings. The release of the pull down winding restores the ratchet device to normal.